LitCovid-sentences  

PMC:7650537 / 1553-27644 JSONTXT 11 Projects

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Id Subject Object Predicate Lexical cue
T13 0-2 Sentence denotes 1.
T14 3-15 Sentence denotes Introduction
T15 16-170 Sentence denotes By the end of the year, 2019, Chinese local health authorities reported the occurrence of a cluster of pneumonia cases in Wuhan in the Hubei Province [1].
T16 171-388 Sentence denotes Shortly after, a novel beta coronavirus—which is now designated as severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) [2]—was discovered in the bronchoalveolar lavage fluid of a patient with pneumonia [1,3].
T17 389-507 Sentence denotes This enveloped virus has a single-stranded positive sense ribonucleic acid (RNA) genome of approximately 30 kilobases.
T18 508-631 Sentence denotes Several surface proteins, known as the spike (S), envelope (E), and membrane (M) proteins, are embedded in a lipid bilayer.
T19 632-911 Sentence denotes These proteins mediate the viral entry (S; S1 unit: binding to host receptor angiotensin-converting enzyme 2 via its receptor binding domain (RBD) and S2 unit: membrane fusion) and are also responsible for viral fusion (M), morphogenesis (E), assembly (E and M), and budding (M).
T20 912-968 Sentence denotes The RNA is associated with the nucleocapsid (N) protein.
T21 969-1052 Sentence denotes The latter plays a role in the viral replication and transcription cycle [4,5,6,7].
T22 1053-1081 Sentence denotes SARS-CoV-2 emerged globally.
T23 1082-1208 Sentence denotes As of 24 September 2020, the World Health Organization reported 31,664,104 SARS-CoV-2 infections and 972,221 deaths worldwide.
T24 1209-1333 Sentence denotes So far, 278,070 cases and 10,982 deaths have been registered for Germany (Robert Koch-Institute, data of 24 September 2020).
T25 1334-1549 Sentence denotes The diagnosis of acute coronavirus-induced disease 2019 (COVID-19) requires the demonstration of SARS-CoV-2 RNA in respiratory samples by real-time reverse transcription polymerase-chain reaction (real-time RT-PCR).
T26 1550-1736 Sentence denotes The specificity of the SARS-CoV-2 real-time RT-PCR has been reported up to 100% [8], while sensitivity under clinical conditions seems to be lower and was roughly estimated with 70% [9].
T27 1737-1914 Sentence denotes More recently, the measurement of the immune response against SARS-CoV-2 came into the focus of clinical diagnostics, particularly by the detection of virus-specific antibodies.
T28 1915-2067 Sentence denotes The use of SARS-CoV-2 antibody tests could clarify the etiology of the disease in patients who present late, after two weeks from the onset of symptoms.
T29 2068-2247 Sentence denotes These tests can also demonstrate the viral spread in the community and may even identify individuals who are potentially protected from reinfection by neutralizing antibodies [8].
T30 2248-2466 Sentence denotes It is believed that the majority of antibodies are raised against the abundant N protein, while antibodies directed against the S protein are considered more specific and correlate with the neutralizing capacity [7,8].
T31 2467-2632 Sentence denotes Earlier works on the antibody response in SARS (2002/2003) patients showed a significantly higher sensitivity of tests based on the N protein as the antigen [10,11].
T32 2633-2779 Sentence denotes The diagnostic value of SARS-CoV-2 antibody tests, however, may be limited due to their potential cross-reactivity with other human coronaviruses.
T33 2780-2866 Sentence denotes So far, the duration of the acquired immunity after a SARS-CoV-2 infection is unclear.
T34 2867-3003 Sentence denotes However, based on experience with reinfections from other human coronaviruses, it remains yet open if the immunity is long-lasting [12].
T35 3004-3258 Sentence denotes Several studies reported a rapid decay of SARS-CoV-2 immunoglobulin G (IgG) in asymptomatic individuals [13] and mild COVID-19 cases [14] but, more surprisingly, also in hospitalized patients presenting with the full clinical spectrum of COVID-19 [5,15].
T36 3259-3363 Sentence denotes Very recently, differences in the kinetics of N- or S-specific IgG came into the focus of research [16].
T37 3364-3587 Sentence denotes While a decline in the IgG directed against the N protein was evident, the response to the S protein or its RBD was found to be more stable [16,17] and was associated with the presence of virus-neutralizing antibodies [17].
T38 3588-3759 Sentence denotes To the best of our knowledge, clinically validated assays for the specific detection of IgG directed against the SARS-CoV-2 surface proteins E and M are not yet available.
T39 3760-3906 Sentence denotes However, it would make sense to investigate such antibody responses as well, since they can also correlate with virus-neutralizing capacities [4].
T40 3907-4053 Sentence denotes In the following, we present data on the diagnostic performance of eight commercially available SARS-CoV-2 IgG or total SARS-CoV-2 antibody tests.
T41 4054-4127 Sentence denotes Variations in their diagnostic sensitivity and specificity were observed.
T42 4128-4300 Sentence denotes In terms of their performance, two IgG assays using the N or S proteins of SARS-CoV-2 were selected for an analysis of follow-up sera to obtain data on the kinetics of IgG.
T43 4301-4418 Sentence denotes The development of IgG avidities and the kinetics of SARS-CoV-2-neutralizing antibodies were also examined over time.
T44 4420-4422 Sentence denotes 2.
T45 4423-4444 Sentence denotes Materials and Methods
T46 4445-4586 Sentence denotes The ethics committee of the Medical Faculty of Kiel University (Kiel, Germany) approved the setting of this study (reference number D467/20).
T47 4588-4592 Sentence denotes 2.1.
T48 4593-4669 Sentence denotes Reference Samples and Tests Chosen for Evaluation of Immunoassay Performance
T49 4670-4781 Sentence denotes Thirty-seven serum samples were obtained from 26 outpatient patients with a PCR-confirmed SARS-CoV-2 infection.
T50 4782-5010 Sentence denotes Blood was drawn between four and 60 days (median 19 days) after a positive real-time RT-PCR result in which parts of the SARS-CoV-2 E or N genes [18] were detected in oropharyngeal swabs with a cycle threshold ≤35 (median 26.8).
T51 5011-5079 Sentence denotes Serum was obtained from the blood and stored at −20 °C until tested.
T52 5080-5260 Sentence denotes These sera are likely to contain SARS-CoV-2 IgG/total antibodies and, therefore, were considered to determine the serological assay sensitivities (as previously suggested by [19]).
T53 5261-5457 Sentence denotes This variant of the sensitivity calculation only took into account whether a SARS-CoV-2-infected patient was reactive at all, regardless of when this reactivity was developed (reference method 1).
T54 5458-5588 Sentence denotes A plaque reduction neutralization assay (PRNT) using a SARS-CoV-2 isolate designated as Kiel M16502/2020 and Vero cells (order no.
T55 5589-5723 Sentence denotes 605372, CLS Cell Lines Service GmbH, Eppelheim, Germany) was included as a further reference for the calculation of the sensitivities.
T56 5724-5784 Sentence denotes All sera classified as reactive in the PRNT were considered.
T57 5785-5839 Sentence denotes This also covered follow-up sera (reference method 2).
T58 5840-5967 Sentence denotes Testing was done under biosafety level 3 conditions and was in accordance to previous reports [20,21] with minor modifications.
T59 5968-6063 Sentence denotes One to two days before infection, 1.0 × 105 cells were seeded into each well of 48-well plates.
T60 6064-6149 Sentence denotes These were then incubated under standard conditions until the cells became confluent.
T61 6150-6509 Sentence denotes Directly prior to the PRNT, patient sera were heat-inactivated at 56 °C for 30 min and then diluted from 1:10 to 1:1280 in cell culture medium consisting of Dulbecco’s modified Eagle’s medium (DMEM) (Bio&SELL GmbH, Feucht, Germany) supplemented with 3.7 g/L NaHCO3, 4.5 g/L glucose, 2 mM L-glutamine, and 1% (v/v) Penicillin/Streptomycin/Fungi-Mix (Bio&SELL).
T62 6510-6689 Sentence denotes A serum dilution series was made by mixing 50 µL of each dilution step with 50 µL virus suspension containing 100 plaque-forming units, followed by an incubation for 1 h at 37 °C.
T63 6690-6877 Sentence denotes The cells were washed with phosphate-buffered saline (Bio&SELL), inoculated with 100 μL of these virus serum dilutions, and incubated for one hour at room temperature on a rocking shaker.
T64 6878-7036 Sentence denotes Then, 100 µL of the cell culture medium supplemented with 20% (v/v) fetal calf serum (FCS) was added to each well to achieve a FCS concentration of 10% (v/v).
T65 7037-7228 Sentence denotes After four to five days, cells were fixed with 4% (w/v) paraformaldehyde in phosphate-buffered saline and stained with an aqueous solution of 0.1% (w/v) crystal violet and 20% (v/v) methanol.
T66 7229-7270 Sentence denotes The stained plates were photo-documented.
T67 7271-7404 Sentence denotes All dilution steps were tested in quadruplicates, and plaque formation was compared to an untreated cell control and a virus control.
T68 7405-7576 Sentence denotes A serum dilution >1:10, which prevented plaque formation in at least 50% of the wells compared to the virus control, was classified as reactive and probably as protective.
T69 7577-7635 Sentence denotes The reciprocal titers were used to visualize the kinetics.
T70 7636-7741 Sentence denotes If an exact titer could not be given, a geometric mean value was calculated from the two adjacent titers.
T71 7742-7893 Sentence denotes For the calculation of assay specificities, 100 archived sera collected during the summer 2018 (N = 50) and during winter 2018/2019 (N = 50) were used.
T72 7894-7960 Sentence denotes None of these sera were expected to contain SARS-CoV-2 antibodies.
T73 7961-8068 Sentence denotes The inclusion of such pre-pandemic sera for the demonstration of specificity was previously suggested [19].
T74 8070-8074 Sentence denotes 2.2.
T75 8075-8113 Sentence denotes Investigated SARS-CoV-2 Antibody Tests
T76 8114-8794 Sentence denotes Seven SARS-CoV-2 IgG assays (Abbott SARS-CoV-2 IgG, Wiesbaden, Germany; DiaSorin Liaison® SARS-CoV-2 S1/2 IgG, DiaSorin, Dietzenbach, Germany; Epitope EDI™ Novel Coronavirus COVID-19 IgG ELISA Kit, Epitope Diagnostics, San Diego, CA, USA; Euroimmun Anti-SARS-CoV-2 ELISA (IgG), EUROIMMUN AG, Lübeck, Germany; Mikrogen recomWell SARS-CoV-2 IgG, Mikrogen GmbH, Neuried, Germany; SARS-CoV-2 ViraChip® IgG Test, Viramed Biotech AG, Planegg, Germany; and SERION ELISA agile SARS-COV-2 IgG, Institute Virion-Serion GmbH, Würzburg, Germany), as well as one total SARS-CoV-2 antibody test (Roche Elecsys Anti-SARS-CoV-2, Roche Diagnostics, Mannheim, Germany), were included in this study.
T77 8795-9017 Sentence denotes The recombinant antigens of these tests cover the N protein (Abbott, Epitope, Mikrogen, Roche) and the entire S protein (Virion-Serion), as well as its S1 domain alone (Euroimmun) or together with the S2 domain (DiaSorin).
T78 9018-9219 Sentence denotes The SARS-CoV-2 ViraChip® IgG test kit uses the purified viral surface antigens S1 and S2 and the N antigen, which are all presented separately at a defined position on a nitrocellulose film (Table S1).
T79 9220-9561 Sentence denotes All tests were conducted strictly following the recommendations of the manufacturers on an Architect or Alinity machine (Abbott), a Liaison XL (DiaSorin), or a Cobas e 411 (Roche) or, for the assays of Epitope, Euroimmun, Mikrogen Viramed, and Virion-Serion, on the BEP 2000 system (Siemens Healthcare GmbH, Erlangen, Germany), respectively.
T80 9562-9671 Sentence denotes The ViraChip® test was then evaluated automatically by help of a ViraChip® reader and the ViraChip® Software.
T81 9672-9730 Sentence denotes All borderline/gray zone results were counted as positive.
T82 9731-9865 Sentence denotes Furthermore, raw data from seven assays were converted into relative indices according to the decision limits set by the manufacturer.
T83 9866-9999 Sentence denotes Thereby, a signal (S)/cut-off (CO) value of <1 was valued as negative and ≥1 as positive, which corresponds to a previous study [22].
T84 10000-10143 Sentence denotes Results of the SARS-CoV-2 ViraChip® IgG could not be converted into relative indices and were only given qualitatively as negative or positive.
T85 10144-10283 Sentence denotes The proportion of correctly identified samples per test relative to the chosen reference method was calculated and given as assay accuracy.
T86 10284-10449 Sentence denotes The convalescent sera were also tested with and without avidity reagent (contains urea in denaturating concentrations) in two versions of an IgG line assay (blot v1:
T87 10450-10519 Sentence denotes Mikrogen recomLine Coronavirus IgG (Avidität), prototype and blot v2:
T88 10520-10570 Sentence denotes Mikrogen recomLine SARS-CoV-2 IgG (Avidität)/RUO).
T89 10571-10794 Sentence denotes The first version is based on the N protein of the human coronaviruses (HCoVs) 229E, HKU1, NL63, and OC43, which are used separately as antigens, and on the N protein of the “classic” SARS-CoV from 2002/2003 and SARS-CoV-2.
T90 10795-10955 Sentence denotes The second improved version still uses the N proteins of the aforementioned HCoVs and of SARS-CoV-2 but has been expanded to include the S1 antigen and its RBD.
T91 10956-11011 Sentence denotes A Dynablot Plus system was used to process all samples.
T92 11012-11121 Sentence denotes Blots were then evaluated automatically with a BLOTrix reader and the recomScan software (all from Mikrogen).
T93 11123-11127 Sentence denotes 2.3.
T94 11128-11211 Sentence denotes Kinetics of SARS-CoV-2 IgG Indices, IgG Avidities, and Neutralizing Antibody Titers
T95 11212-11364 Sentence denotes The SARS-CoV-2-IgG course was examined in 11 of the 26 SARS-CoV-2-infected patients over a period of up to 165 days after the first positive PCR result.
T96 11365-11520 Sentence denotes For this purpose, the N- and S-specific IgG assays were selected, which showed the optimal performance depending on sensitivity, specificity, and accuracy.
T97 11521-11622 Sentence denotes The sera were also tested in the improved IgG line assay, including the determination of the avidity.
T98 11623-11813 Sentence denotes The course of the virus-neutralizing titers was examined in the PRNT (including the retesting of samples from the validation part of this study in order to show the assays’ reproducibility).
T99 11814-11890 Sentence denotes An attempt was made to investigate all samples of a patient in one test run.
T100 11891-12019 Sentence denotes Follow-up samples from five routine patients, including four family members from a SARS-CoV-2-infected case, were also examined.
T101 12021-12023 Sentence denotes 3.
T102 12024-12031 Sentence denotes Results
T103 12033-12037 Sentence denotes 3.1.
T104 12038-12097 Sentence denotes Performance of Eight SARS-CoV-2 IgG or Total Antibody Tests
T105 12098-12246 Sentence denotes Thirty-seven samples taken from patients with a PCR-confirmed SARS-CoV-2 infection were analyzed with eight SARS-CoV-2 IgG or total antibody assays.
T106 12247-12390 Sentence denotes Samples #1, #7, and #9 were taken nine days before to four days after PCR and were all found to be free of SARS-CoV-2 antibodies by the assays.
T107 12391-12503 Sentence denotes These samples were not considered for calculation of the sensitivity but demonstrated seroconversion (Figure 1).
T108 12504-12604 Sentence denotes Out of the remaining 34 samples, only one serum (#20; Figure 1), which was obtained from patient no.
T109 12605-12714 Sentence denotes 12 ten days after a positive RT-PCR, tested negative for SARS-CoV-2 IgG/total antibodies in the eight assays.
T110 12715-12763 Sentence denotes However, this sample exhibited a PRNT 1:10–1:20.
T111 12764-12829 Sentence denotes All other samples were reactive in at least one assay (Figure 1).
T112 12830-12945 Sentence denotes Twenty (76.9%) patients developed virus-neutralizing antibodies, as shown by a PRNT >1:10 (Figure 1 and Figure S1).
T113 12946-13087 Sentence denotes With respect to the SARS-CoV-2 PCR (reference 1) or the PRNT results (reference 2), assay sensitivities ranged from 80.8% to 96.3% (Table 1).
T114 13088-13188 Sentence denotes Specificity was calculated using 100 archived samples that should not contain SARS-CoV-2 antibodies.
T115 13189-13245 Sentence denotes A total of ten sera were reactive in one or more assays.
T116 13246-13321 Sentence denotes None contained SARS-CoV-2 neutralizing antibodies (Figure 2 and Figure S1).
T117 13322-13467 Sentence denotes The residual 90 stored samples were not tested in the PRNT, as they were found to be free of SARS-CoV-2 IgG/total antibodies in all eight assays.
T118 13468-13573 Sentence denotes Thus, assay specificities ranged from 96.0% to 100%, and accuracies varied from 93.7% to 99.2% (Table 1).
T119 13574-13728 Sentence denotes Twelve routine samples obtained from individuals who were interested in their SARS-CoV-2 antibody status were re-evaluated by all eight assays (Figure 3).
T120 13729-13810 Sentence denotes Six of them—including three family members of the SARS-CoV-2-infected patient no.
T121 13811-13909 Sentence denotes 14 (Figure 1)—were classified SARS-CoV-2 IgG/total antibody-positive by the majority of the tests.
T122 13910-13968 Sentence denotes Isolated reactivity was observed in three sera (Figure 3).
T123 13969-14150 Sentence denotes Twenty-four (92.3%) of the 26 SARS-CoV-2 infected patients were reactive in one or both versions of the IgG recomLine assay; the test results differed only in three sera (Figure 1).
T124 14151-14385 Sentence denotes One out of the ten archived sera that were reactive in at least one of the SARS-CoV-2 IgG/total antibody tests was also classified as SARS-CoV-2 IgG-positive by the prototype immunoblot (v1) but was negative in the improved version 2.
T125 14386-14636 Sentence denotes The underlying sample #7 was collected in the winter 2018/2019 and was found to be reactive for SARS-CoV-2 IgG/total antibodies by the Mikrogen (S/CO 1.33), Roche (S/CO 3.46), and Viramed (N antigen 125 ViraChip® Units) assays in parallel (Figure 2).
T126 14637-14813 Sentence denotes The twelve routine samples were analyzed by both versions of the blot (v1: nine samples and v2: all samples), and results of the immunoassays were largely confirmed (Figure 3).
T127 14815-14819 Sentence denotes 3.2.
T128 14820-14905 Sentence denotes Kinetics of SARS-CoV-2 IgG, Development of IgG Avidities, and Neutralizing Antibodies
T129 14906-15132 Sentence denotes In the validation part of our study, the Abbott assay, which is based on the SARS-CoV-2 N as the epitope, and the Virion-Serion assay, which uses S as the antigen, proved to be the most sensitive and specific assays (Table 1).
T130 15133-15288 Sentence denotes Therefore, both were selected to study the kinetics of SARS-CoV-2 IgG in eleven patients and five individuals (including four family members of patient no.
T131 15289-15318 Sentence denotes 14) from routine diagnostics.
T132 15319-15422 Sentence denotes The median of the last sample submission was 153 days after the PCR, the range between 80 and 165 days.
T133 15423-15491 Sentence denotes Results from the validation part of this study were also considered.
T134 15492-15549 Sentence denotes N-specific IgG antibodies were detectable in all persons.
T135 15550-15708 Sentence denotes Two groups of individuals were evident: one group of six patients showed relatively stable IgG levels over time, while the other showed a short-term decrease.
T136 15709-15818 Sentence denotes Accordingly, the indices of six individuals fell below the limit of positivity during the observation period.
T137 15819-15906 Sentence denotes A stable S-specific IgG response was demonstrated in almost all individuals (Figure 4).
T138 15907-15937 Sentence denotes Only two subjects (patient no.
T139 15938-15956 Sentence denotes 22 and routine no.
T140 15957-16011 Sentence denotes 5) showed a drop in IgG below the limit of positivity.
T141 16012-16034 Sentence denotes The routine sample no.
T142 16035-16139 Sentence denotes 5 still possessed isolated reactivity against the N antigen in the improved line assay (data not shown).
T143 16140-16287 Sentence denotes In the latter test, three patients developed SARS-CoV-2-specific IgG of high avidity after 65–130 days, which was confirmed in consecutive samples.
T144 16288-16332 Sentence denotes The pattern of reactivity differed slightly:
T145 16333-16486 Sentence denotes Two patients developed IgG of high avidity against the RBD and S1 epitopes, while the third showed isolated reactivity against the N antigen (Figure S3).
T146 16487-16642 Sentence denotes Presence of SARS-CoV-2-neutralizing antibodies over several months was demonstrated in eight (72.7%) SARS-CoV-2 patients and a family member of patient no.
T147 16643-16651 Sentence denotes 14 (R4).
T148 16652-16734 Sentence denotes However, only one of them developed a stable titer >1:40 (Figure 5 and Figure S2).
T149 16735-16886 Sentence denotes Retests of sera that were already included in the validation part of this study showed an excellent reproducibility of the PRNT (R2 = 0.96, Figure S4).
T150 16888-16890 Sentence denotes 4.
T151 16891-16901 Sentence denotes Discussion
T152 16902-17016 Sentence denotes In a rather short period, various assays for the detection of SARS-CoV-2 antibodies were introduced to the market.
T153 17017-17182 Sentence denotes A meta-analysis of 38 studies on the performance of different format SARS-CoV-2 antibody tests mainly manufactured from Chinese companies was reported recently [23].
T154 17183-17374 Sentence denotes Furthermore, studies on the sensitivity and specificity of SARS-CoV-2 IgG tests, including ELISAs from the Epitope, Euroimmun, and Mikrogen companies, were published previously [20,21,22,24].
T155 17375-17685 Sentence denotes A recent prospective study examined the sensitivity of seven antibody tests from Abbott, Euroimmun, Mediagnost, Novatec, Virotech, Roche, and Siemens companies but did not provide data on their specificities or on the correlation of the assay results to the presence of SARS-CoV-2-neutralizing antibodies [25].
T156 17686-17829 Sentence denotes Here, we analyzed the diagnostic performance of eight commercially available tests, all of which have been released within the past few months.
T157 17830-18009 Sentence denotes These were compared to identify appropriate tests to study the kinetics of N- or S-specific SARS-CoV-2 IgG or total antibodies in outpatients with a previous SARS-CoV-2 infection.
T158 18010-18085 Sentence denotes To our knowledge, such a comprehensive study has not been conducted before.
T159 18086-18217 Sentence denotes Three assays (Abbott, DiaSorin, and Roche) were applied in a random-access manner, which reduced the needed hands-on-time markedly.
T160 18218-18321 Sentence denotes Convalescent sera from 26 SARS-CoV-2-infected patients were used to investigate the test sensitivities.
T161 18322-18563 Sentence denotes These samples were characterized by a previous positive SARS-CoV-2 PCR result of the donors (reference method 1) and may possess SARS-CoV-2-neutralizing capacities (>1:10), as demonstrated in a laboratory-developed PRNT (reference method 2).
T162 18564-18678 Sentence denotes Furthermore, two versions of an immunoblot, including the determination of SARS-CoV-2 IgG avidities, were applied.
T163 18679-18914 Sentence denotes With respect to the previous positive SARS-CoV-2 PCR result considered as the reference of first choice, following a recent suggestion [19], assay sensitivities were found to be relatively high and varied from 80.8% to 96.2% (Table 1).
T164 18915-19007 Sentence denotes This finding is in accordance to other studies [21,22,24,25,26] and to a meta-analysis [23].
T165 19008-19272 Sentence denotes Six (23.1%; five, 19.2%, if the positive retesting result of the initial serum from patient 4 is taken into account; for details, see below) of the 26 SARS-CoV-2-infected patients did not develop SARS-CoV-2-neutralizing antibodies, as demonstrated by a PRNT ≤1:10.
T166 19273-19465 Sentence denotes Among them were two individuals who were only recognized as IgG-positive in the Abbott and Virion-Serion assays and were partially reactive in the ViraChip® and the IgG immunoblots (Figure 1).
T167 19466-19548 Sentence denotes This confirms a previous report of a high sensitivity of the Abbott IgG test [27].
T168 19549-19749 Sentence denotes The absence of neutralizing antibodies in several COVID-19 patients was also reported by others [28] and may be associated with the mild course of the infection mainly observed in outpatient patients.
T169 19750-19943 Sentence denotes However, since no clinical data were available to us, a severe underlying disease or a serious course of the SARS-CoV-2 infection cannot be ruled out in the individuals of our study collective.
T170 19944-20058 Sentence denotes Recently, presence of neutralizing antibodies was found to be associated with protection against reinfection [29].
T171 20059-20242 Sentence denotes If the PRNT was chosen as another reference (Figure S1), sensitivities varied from 88.9% to 96.3% (Table 1), which is largely comparable to the results obtained with the first method.
T172 20243-20476 Sentence denotes These sensitivities can be even higher, as retesting of the initial serum from patient 4 in the second part of our study revealed the presence of low-level neutralizing antibodies (1:10 vs. 1:20–1:40; Figure 5 and Figures S1 and S2).
T173 20477-20671 Sentence denotes With respect to a sample from patient 1 taken six days after the PCR, two S-based assays failed to detect SARS-CoV-2 IgG, while all assays that used the N as an epitope were reactive (Figure 1).
T174 20672-20783 Sentence denotes Thus, usage of the latter may lead to the detection of IgG/total antibodies at an earlier stage post-infection.
T175 20784-20942 Sentence denotes Furthermore, a lack of reactivity in some assays using the S antigen does not necessarily mean that SARS-CoV-2-neutralizing antibodies are missing (Figure 1).
T176 20943-21012 Sentence denotes Seroconversion was clearly demonstrated in three patients (Figure 1).
T177 21013-21145 Sentence denotes The majority of SARS-CoV-2 IgG in sera from SARS-CoV-2-infected patients were verified by both versions of an immunoblot (Figure 1).
T178 21146-21251 Sentence denotes The latter can be used to differentiate the antibody reactivities against individual SARS-CoV-2 antigens.
T179 21252-21422 Sentence denotes The specificities of the SARS-CoV-2 IgG/total antibody tests are at comparatively high levels between 96.0% and 100.0%, as has also been reported by others [21,22,24,26].
T180 21423-21631 Sentence denotes Interestingly, one sample collected in the winter 2018/2019 was found to be reactive in the Mikrogen, Roche, and Viramed assays, as well as in the prototype immunoblot, but could not be confirmed by the PRNT.
T181 21632-21836 Sentence denotes For all other 99 archived samples, a random pattern of rare, isolated reactivity was demonstrated, and none was confirmed as possessing SARS-CoV-2-neutralizing antibodies by PRNT (Figure 2 and Figure S1).
T182 21837-21945 Sentence denotes Potential cross-reactivity with the HCoVs responsible for common colds may therefore not be a major problem.
T183 21946-22151 Sentence denotes The analysis of the immunoblot results shows, however, that sera from SARS-CoV-2-infected patients may simultaneously react with the antigens from HCoVs 229E, HKU-1, NL63, OC43, and SARS-CoV-2 (Figure S3).
T184 22152-22342 Sentence denotes Due to the currently estimated low prevalence of SARS-CoV-2 IgG in the overall German population, even high specificities of 96–98% would produce a relevant number of false positive results.
T185 22343-22496 Sentence denotes Thus, such assays, which all show an accuracy over 93%, should be preferentially used for the testing of patients with a history of a probable infection.
T186 22497-22603 Sentence denotes In the case of doubt, the implementation of the labor-intensive and time-consuming PRNT may be considered.
T187 22604-22853 Sentence denotes The kinetics of SARS-CoV-2 IgG was studied up to 165 days after positive SARS-CoV-2 PCR results by the analysis of consecutive samples from 11 patients and samples from five routine patients; four are family members of a SARS-CoV-2-infected patient.
T188 22854-22981 Sentence denotes The results were obtained with two IgG assays based on the N (Abbott) or the entire S (Virion-Serion) antigens as the epitopes.
T189 22982-23106 Sentence denotes Both tests turned out to be the most sensitive and specific assays in the validation part of our study (compare in Table 1).
T190 23107-23182 Sentence denotes Thereby, SARS-CoV-2-specific antibodies were detectable in all individuals.
T191 23183-23427 Sentence denotes While the N-based IgG assay revealed the existence of two groups of individuals, and one of them showed a rapid decrease of IgG indices within a few months, the IgG reactivity in the S protein-based assay was found to be more stable (Figure 4).
T192 23428-23611 Sentence denotes This is in-line with a previous preprint [16] and could suggest that the latter test is better suited for epidemiological studies, especially when it comes to questions of prevalence.
T193 23612-23717 Sentence denotes Accordingly, the majority of SARS-CoV-2-infected patients in our study developed neutralizing antibodies.
T194 23718-23840 Sentence denotes The titers were stable during the observation period but were in a relatively low range between >1:10 and 1:80 (Figure 5).
T195 23841-23931 Sentence denotes Only three patients showed conversion from low to high SARS-CoV-2 IgG avidity (Figure S3).
T196 23932-24043 Sentence denotes The limited number of included SARS-CoV-2 patients, however, limits the informative value of the present study.
T197 24044-24290 Sentence denotes The evaluability of the simple and reproducible PRNT technique applied here may be improved by overlaying the cells with cellulose or by using specific antibodies to detect the remaining viral antigens in the cells, as reported previously [7,20].
T198 24291-24474 Sentence denotes Furthermore, the application of a modified cytopathic effect inhibition assay [30] may be useful to facilitate standardization and quantification and will be valued in future studies.
T199 24475-24629 Sentence denotes Several SARS-CoV-2-infected patients and routine patients in our study lost their SARS-CoV-2 (N)-specific IgG within a few months or could lose them soon.
T200 24630-24809 Sentence denotes These individuals can theoretically be prone to reinfection, especially since the S-specific IgG and the neutralizing antibodies are stable but only present in low indices/titers.
T201 24810-24852 Sentence denotes In a few patients, both were undetectable.
T202 24853-24977 Sentence denotes However, this view does not take into account the booster effect that can be expected in the event of renewed virus contact.
T203 24978-25045 Sentence denotes This would most likely lead to a rapid increase in antibody titers.
T204 25046-25188 Sentence denotes Accordingly, vaccine strategies against SARS-CoV-2 may need boosting to maintain sufficient neutralizing antibody titers over a long time [5].
T205 25189-25304 Sentence denotes Waning antibody titers and reinfections are known from various HCoVs mainly responsible for common colds [5,12,31].
T206 25305-25397 Sentence denotes Recently a well-documented case of an asymptomatic SARS-CoV-2 reinfection was reported [32].
T207 25398-25515 Sentence denotes In our opinion, the importance of such rare events for the progression of the temporary pandemic appears to be minor.
T208 25516-25621 Sentence denotes Nevertheless, a permanent presence of measurable SARS-CoV-2 IgG in the serum of all patients is unlikely.
T209 25622-25778 Sentence denotes This is not surprising and has also been observed in patients after infections with SARS-CoV (2002/2003) or Middle East respiratory syndrome (MERS)-CoV [5].
T210 25779-25873 Sentence denotes It does not necessarily mean that these individuals will be susceptible to severe reinfection.
T211 25874-26010 Sentence denotes Future studies should now address the virus-specific antibody response on the mucous membranes, as well as the cellular immune response.
T212 26011-26091 Sentence denotes For this, the development of valid routine test procedures is urgently required.